The present invention relates to a photonic component comprising at least one linear optical waveguide, a so-called active portion of which is surrounded over all or part of its periphery by a group of one or more essentially semiconducting nanotubes. These nanotubes interact with their external environment in an active zone extending on either side of the optical waveguide, so as to thus induce an optical coupling between an electrical or optical signal applied to the nanotubes and on the other hand an optical signal in the active portion of the waveguide. Such a component can carry out in particular bipolar electro-optical functions as light source, or modulator or detector, inside the optical guide, for example with an electro-optical coupling between on the one hand an electrical signal applied between the electrodes, and on the other hand an optical signal emitted or modified in the active portion of the optical waveguide towards the remainder of said optical guide.
It also relates to an electronic and optical hybrid integrated circuit the optical and electronic circuits of which interact with each other through at least one such electro-optical component; as well as to a method for the production of such a component or integrated circuit.
The invention relates to the field of nanophotonics and optoelectronics for various applications: for example optical interconnections in future integrated circuits, optical telecommunications, biophotonics, labs-on-a-chip, etc.
Components
Numerous systems use optical circuits in order to process or transmit digital data, for example for telecommunications or in computer equipment. So-called electro-optical or optronic components are used to generate information in these optical circuits and allow them to interact with electronic circuits.
These components include different types and in particular light sources, detectors, and modulators.
Such a light source uses electrical energy to produce a light, coherent (laser) or not, which can be injected into an optical waveguide to supply an optical circuit. Nowadays such light sources are often made of type III-V semiconductor materials.
An electro-optical modulator receives an electrical signal and acts on a light flux in order to modulate it as a function of the electrical signal and thus provide a light signal, for example in order to convert an electrical telecommunication signal into an optical signal which is injected into a long-distance or even transoceanic optical telecommunication fibre. Nowadays such modulators are often made of III-V semiconductor.
Such a detector receives a light flux or signal, and produces an electrical signal as a function of the light signal received, for example in order to decode an optical signal received from an optical fibre and convert it into an electrical signal which can be processed by a computer. Nowadays such detectors are often produced based on germanium or InGaAs.
A greater compactness of the circuits and components is useful for increasing the density of the circuits and therefore the miniaturization and/or the performance of the equipment that they make it possible to produce.
It is useful to be able to integrate together as many components and/or sub-assemblies as possible. This makes it possible for example to reduce the costs, but also to increase the density and the miniaturization of the circuits, and to reduce the interfaces between blocks and reduce consumption and heating of the circuits obtained.
Optical and Electronic Hybrid Integrated Circuits
Optical or optoelectronic integrated circuits are increasingly used in numerous fields.
For example, they are a possible solution to the limitations increasingly affecting the development of purely electronic components which exhibit constraints proving increasingly problematic and sometimes insurmountable.
In fact, as the density of integration of the components increases as the size of the transistors decreases, the interconnections are increasingly complex, and existing circuits possess more than 12 metal/dielectric levels used to produce communication channels between different sets of transistors within the same integrated circuit.
In a few years from now, it can be foreseen that the performances of the integrated circuits will be limited due to the growing complexity of these connection circuits. This limitation will in particular affect metal interconnections, for example due to the time constant associated with the resistive and capacitive values of these connections, or due to the skin effect in the conductors which will accentuate these limitations at high frequency causing increasing distortion of the signals and an increase in the propagation delays. The overall links within an integrated circuit, such as the connections between blocks and the distribution of the clock signal, are among the first affected by these limitations.
Solutions are sought for pushing back these limits in existing technologies by the introduction of conductors having less resistivity and materials having a lower dielectric constant, or by introducing repeaters placed regularly along the connection lines. These solutions are however term-limited, and can moreover increase the space requirement of the circuits as well as their electricity consumption and therefore their heating.
One type of solution proposed consists of using optical interconnections, which provides a certain number of advantages:                Performances are virtually independent of the length of the interconnections;        Propagation is not very dependent on the signal frequency;        The repeaters are not necessary which results in a saving in space and in dissipated power;        Distribution does not generate noise towards the remainder of the chip;        It is possible to use several wavelengths on the same channel: wavelength multiplexing.        
The utilization of such optical interconnections involves the integration of electro-optical components within electronic integrated circuits, such as sources, modulators and light-signal detectors. The solution currently envisaged in order to be compatible with CMOS circuits technology is to guide the light in the silicon film of a silicon-on-insulator (SOI) substrate, to modulate the light using silicon- or SiGe-based modulators, to detect it using germanium and to emit the light using mainly III-V semiconductors.
The internal high frequency optical link in an integrated circuit on silicon currently considered in the profession is thus mainly made up of three materials: silicon, germanium and III-V.
However, such an optical link structure requires very heterogeneous integration as regards the materials and manufacturing processes used as well as in terms of design and internal organization of the integrated circuit. This heterogeneity has numerous drawbacks for example and in particular as regards design flexibility and manufacturing simplicity with a limiting factor as regards the source based on III-V semiconductor which does not use the same substrate dimensions.
Moreover, these current architectures of electro-optical components limit their miniaturization, for example due to the necessary interaction lengths within optical guides which are sometimes several millimeters.
These architectures and the stringent accuracy requirements that they involve, as well as the differences in materials that they use, make the integration of these components within integrated circuits complex and expensive. This limits in particular the possibilities of hybrid integration combining optical integrated circuits and electronic integrated circuits together within the same “chip” or integrated circuit.
Use of Nanotubes
Studies of nanotubes have shown that these materials can have certain semiconductor-type properties due to their nanometric scale, and their one-dimensional nature.
Thus, the publication “Electroluminescence from Single-Wall Carbon Nanotube Network Transistors” by Adam et al. in NanoLetters 2008, 8 (8) 2351-2355, presents a multidirectional electroluminescent effect obtained in a field-effect transistor produced by applying an electric field between several successive parallel electrodes arranged across a track constituted either by a single nanotube (CNFET), or by a unorganized network of several nanotubes (NNFET).
In the publications “Carbon Nanotubes and Optical Confinement—Controlling Light Emission in Nanophotonic Devices” by Steiner et al. in SPIE 2008 Vol. 703713 703713, and “A microcavity-controlled, current-driven, on-chip nanotube emitter at infrared wavelengths” by Fengnian et al. in Nature Nanotechnology Vol. 3 Oct. 2008, it has been proposed to capture such an electroluminescent effect using an optical “amplification” microcavity.
As illustrated below in FIG. 1, this microcavity is formed by two mirrors surrounding an assembly constituted by a layer of SiO2 supporting a layer of PMMA between two side electrodes which are linked to each other by a single nanotube embedded in the PMMA. This cavity is mounted on a layer of P+ doped silicon in order to form a field-effect transistor (FET) producing a light which is captured and amplified by the cavity and re-exits from it perpendicularly to the different superimposed layers.
Similarly, according to the publication “Efficient narrow-band light emission from a single carbon nanotube p-n diode” by Müller et al. in Nature Nanotechnology Letters of November 2009 (DOI: 10.1038/nnano.2009.319), the emission is produced by an individual nanotube mounted in a diode between two zones of electrodes and subjected to an electric field above an optical microcavity.
This prior art describes only light production elements which also have certain drawbacks. Thus, the intensity emitted by these elements is rather low, and is not directional. The microcavity can make it possible to obtain a directional source, but at the price of additional complexity which is likely to impose problematic constraints, in particular for integration. Moreover, the injection of this light into an optical waveguide requires additional adjustments not yet addressed which are themselves also sources of additional complexities, perhaps also of losses in yield or light intensity. These complexities, as well as the direction of emission perpendicular to the layers of the cavity, make any attempt at integration of such components within an optical circuit more complex and difficult, and even more so within a hybrid integrated circuit.
Similarly, a coupling described in the document US 2005/249249 consists of injecting a light produced by a nanotube mounted in an FET transistor into the end of an optical fibre, through a lens arranged on the optical axis of this fibre; or enclosing this nanotube within this optical fibre. Such an assembly however yields little light and is difficult and cumbersome to produce and to adjust, and is ill-suited for use in an integrated circuit.
Generally, a tendency in the state of the art is to use nanotubes for their semiconductor properties. Thus, everything is done to seek to obtain isolated nanotubes, for example a sonic separation in order to avoid bundles of nanotubes, followed by a technique of individual coating with a surfactant product. Such an individual nanotube can then be arranged on a substrate which makes it possible to ensure an electric contact at both its ends by covering the latter with conducting layers forming electrodes.